1. Field of the Invention
The present invention relates to a hydraulic system having a pressure accumulator. More particularly this invention concerns the monitoring of the operation of an accumulator associated with a percussion hammer.
2. Description of the Prior Art
It is standard to power a periodically operating hydraulic tool, for instance a percussion hammer used in a mining operation, from a pump source that supplies liquid at a generally constant pressure and/or volume whose average rate is sufficient to operate the tool but which lies well below the peak rate the tool consumes. For instance the percussion hammer consumes a substantial amount of hydraulic fluid on its forward stroke and on its return stroke only a little. Accordingly it is standard to connect a pressure accumulator to the pressure user to store up the fluid during the part of the cycle when consumption is low and feed it to the user during the part of the cycle when consumption is high.
Thus as seen in FIG. 1 where volume D is plotted on the ordinate and time t on the abscissa, a supply pump produces a constant output Do. The user, however, consumes fluid at a rate shown by the square-wave trace t that lies wholly above the abscissa and that is roughly bisected by the line of output Do. During the cycle halves QA of low consumption the accumulator stores up the fluid from the pump, and during the high-consumption cycle halves QR it feeds this fluid to the user.
The accumulator typically is formed as a substantially closed chamber subdivided by an impermeable but flexible membrane into a compartment that is pressurized with an inert gas, typically nitrogen, at superatmospheric pressure, and a compartment that is connected to the conduit between the pump and the user. When the accumulator becomes damaged or for some reason--leakage, improper filling, valve failure--loses pressure, the effect on the tool is often extremely damaging in that hydraulic shocks that are propagated in the tool and lines that can easily lead to mechanical failure. Unfortunately in the case of a hydraulic percussion hammer used for mining such failure is not rare and is often not noticed immediately because the hammer itself is carried on an arm extending some distance from the tractor and is therefore at some distance from the operator of the machine.
It has been suggested to provide a pressure sensor on the accumulator, typically mounted right on the hammer, and to connect it via a hydraulic or electric line back to a warning device at the operator's station. This solution just adds to the complexity of the piece of equipment and requires that yet another carefully shielded line be extended from the operator to the tool.